1. Field of the Invention
The invention relates to a self-contained, gas-generating, electrochemical cell. The invention further relates to a dispensing device, in particular a device where oxygen gas released from a solid state electrochemical cell increases in pressure to press fluid from a bladder within a chamber through an outlet of the device in a steady continuous flow until the fluid contents of the bladder are exhausted.
2. State of the Art
Richter in U.S. Pat. No. 3,894,538 disclosed a device for dispensing medicines to man or beast. The medicine was contained in a flexible container which became compressed as fluid was electro-osmotically introduced into an adjacent flexible chamber or when gas was electrolytically produced using precious metal electrodes and an unspecified fixed electrolyte. The rate of medicine discharge was to be regulated using a potentiometer.
Maget in U.S. Pat. No. 4,522,698 disclosed electrochemical prime movers. Embodiments of the invention include a device for dispensing pharmaceuticals to a human body over a substantial period of time at a sustained very low rate, where a battery provides the driving force to transport an electrochemically active gas from a precharged chamber to a second chamber, where an ion-exchange membrane separates the two chambers; or where the battery provides the driving force to transport oxygen from air across an ion-exchange membrane to a chamber. Pressure in a chamber increases as electroactive gas transports across the membrane, this increase in pressure drives a piston which forces the contained pharmaceutical fluid to flow through an outlet. The invention requires electrodes which are electrically conductive and act as catalyst to convert molecules to ions; titanium-palladium alloy or palladium black are recommended materials. A controller is utilized to control the magnitude and time pattern of current and voltage applied to the membrane as well as to turn current on and off. To function, the invention requires either exposure to air or precharging with an electroactive gas.
Maget in U.S. Pat. No. 4,886,514 disclosed electrochemically driven drug dispensers. A potential from an external power source drives an electrochemically active gas such as hydrogen or oxygen to be transported across a membrane from a fixed volume chamber to a chamber which has a variable volume. The volume of the chamber varies by either flexing an expansible diaphragm type wall or by displacing a sliding wall, said wall is shared by a second variable volume chamber which contains a fluid drug to be administered. As the electrochemically active gas is transported to the first variable volume chamber, the drug is forced out of the second variable volume chamber through an outlet. Countering the electrochemical transport of gas across the membrane, the gas diffuses in the opposite direction across the membrane in accordance to the pressure gradient and diffusivity properties of the membrane. A controller compensates for the gas diffusion rate and varies the voltage and current to achieve the desired drug delivery rate in a steady or intermittent mode. To function, the invention requires precharging with an electroactive gas.
Maget et al. in U.S. Pat. No. 4,902,278 disclosed a fluid delivery micropump. The pump utilizes an air-actuated battery in a fixed closed circuit with an electrochemical cell which drives the transport of oxygen in air across a membrane. The transport applies external pressure to a collapsible reservoir filled with fluid, as a result, fluid is expelled from the reservoir through an outlet. The membrane is preferably a Nafion material (a perfluoro sulfonic polymer) which has been coated with platinum black/10% Teflon. Electrodes are preferably titanium screens. To control the current, a resistor is utilized. The device is activated by removing a protective peel tab to expose air inlet ports to the battery cathode. A disadvantage of this type of system is that shelf life of the device is dependent on the integrity of the seals which prevent air leakage to the battery. If the seals are not perfect, the battery will slowly discharge before the desired time of use. To function, the invention requires exposure to air.
Winsel in U.S. Pat. No. 5,242,565 disclosed "a device for electrochemical generation of gases for the transportation of fluids and similar mediums." Winsel discloses two approaches. In one approach, the device is constructed very similar to a zinc-air battery. To function, the device must be operated in total absence of oxygen, then it will release hydrogen in a controlled manner. This approach has two disadvantages: 1) in many applications hydrogen is undesirable to collect because it is difficult to contain in a flexible bladder and also is flammable, 2) maintaining an oxygen-free condition is very difficult since most flexible bladder materials are somewhat permeable to oxygens. The other approach which is disclosed by Winsel again is similar to a zinc-air battery except that instead of zinc in the cathode, a reducible oxide or nitrate is present with an alkaline electrolyte. This approach has the advantage that oxygen is released instead of hydrogen; however, cells with alkaline electrolytes are difficult to seals thus a safety hazard may be present or unreliability may result. A description of and explanation for alkaline electrolyte creepage are presented in "Why Alkaline Cells Leak," M. Hull and H. James; J. Electrochem. Soc., March 1977, pp. 332-339.
The prior art includes several devices which are capable of performing the general function of the device presently disclosed; however, the prior art has not satisfied a demand which exists for a device which 1) has a design which can dispense a fluid over a nearly constant rate for an extended period of time, 2) has a simple design which is conducive to fabrication, 3) does not require exposure to air, fluid or the precharging of an electrochemically active gas to fiction.
The present device disclosed is particularly distinguished from the prior art in that the device can function while completely sealed from its external environment, excluding the outlet port through which the fluid will be dispensed and without requiring an internal reservoir of gas to be pumped. Although an organic ion-exchange membrane is utilized in this device, this device is less sensitive to changes in ambient humidity because the membrane is sealed from the environment. Also, the device does not rely on access to air or other gas to operate nor must precautions be taken to avoid the presence of particular gases such as oxygen. The present device also does not utilize an alkaline electrolyte and is distinguished frown the prior art where such electrolyte is difficult to contain. The present device may utilize an electrolyte which is substantially neutral in pH or only slightly acidic, thus posing a reduced safety threat in the event that the contents were released. Further, because the device is simply structured and is comprised of readily available, easily fabricated materials, it is disposable.